Planar Ceramic Membrane Assembly And Oxidation Reactor System

ABSTRACT

Planar ceramic membrane assembly comprising a dense layer of mixed-conducting multi-component metal oxide material, wherein the dense layer has a first side and a second side, a porous layer of mixed-conducting multi-component metal oxide material in contact with the first side of the dense layer, and a ceramic channeled support layer in contact with the second side of the dense layer. The planar ceramic membrane assembly can be used in a ceramic wafer assembly comprising a planar ceramic channeled support layer having a first side and a second side; a first dense layer of mixed-conducting multi-component metal oxide material having an inner side and an outer side, wherein the inner side is in contact with the first side of the ceramic channeled support layer; a first outer support layer comprising porous mixed-conducting multi-component metal oxide material and having an inner side and an outer side, wherein the inner side is in contact with the outer side of the first dense layer; a second dense layer of mixed-conducting multi-component metal oxide material having an inner side and an outer side, wherein the inner side is in contact with the second side of the ceramic channeled layer; and a second outer support layer comprising porous mixed-conducting multi-component metal oxide material and having an inner side and an outer side, wherein the inner side is in contact with the outer side of the second dense layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 10/394,620, filed on Mar.21, 2003, the specification and claims which are incorporated byreference and made a part of this application.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract No.DE-FC26-97FT96052 between Air Products and Chemicals, Inc. and the U.S.Department of Energy. The Government has certain rights to thisinvention.

BACKGROUND OF THE INVENTION

Oxygen can be separated from oxygen-containing gases by mixed-conductingceramic membranes operating at high temperatures wherein the membranesconduct both oxygen ions and electrons. Oxygen gas is produced on thepermeate side of the membrane and can be recovered as a high-purityproduct. Alternatively, the permeated oxygen can be reacted directlywith a hydrocarbon-containing gas, either catalytically ornon-catalytically, to yield a hydrocarbon oxidation product. Variousoxygen-containing gases, such as air, can be used and numerousalternative hydrocarbon oxidation products are possible depending on theoperating conditions and catalyst if used.

There is a significant and growing commercial interest in the productionof synthesis gas from natural gas and air using mixed-conducting ceramicmembrane reactor systems. This technology is presently in thedevelopment stage and commercial applications are envisioned in futureyears as the technology matures. Mixed-conducting ceramic membranereactor systems produce synthesis gas by the partial oxidation ofmethane to form the synthesis gas components CO, H₂, CO₂, and H₂O. Theprocess is carried out by introducing a methane-containing feed gas andan air feed gas into the membrane reactor system, contacting one surfaceof the membrane with methane, and contacting the other surface with air.Oxygen permeates through the membrane, methane reacts with permeatedoxygen to form a methane/synthesis gas mixture, and methane is furtherconverted into synthesis gas as the mixture travels through the reactorwhile reacting with additional permeated oxygen.

This process can be integrated favorably with upstream and downstreamprocesses if the methane/synthesis gas stream is at a high pressure,typically 250-450 psig. In addition, process economics are mostfavorable if the air is at a low pressure, typically less than 50 psig.Therefore, the membranes in the membrane reactor system must be designedto withstand a significant pressure differential between the air sideand the methane/synthesis gas side. To achieve high oxygen fluxesthrough the membrane, the active separating layer of the membrane shouldbe thin, typically less than 200 microns. However, a freestandingmembrane of this thickness could not withstand a typical pressuredifferential of 200-400 psid, and the thin separating layer thereforemust be structurally supported in some fashion.

Various designs for ceramic oxygen-conducting membrane systems capableof withstanding high pressure differentials have been described in theart. For example, a tubular ceramic membrane can be subjected to highpressure methane on one side and low pressure air on the other side, butsuch a membrane must have a sufficiently thick wall to withstand thepressure differential; as a consequence, this membrane cannot achieve ahigh oxygen flux. To address this problem, composite tubular membraneshave been developed which incorporate a thin, dense oxygen-permeatinglayer on a thicker porous support.

Flat plate membrane configurations have been described in the artwherein the active separating layer is supported by a porous layer orlayers on the low pressure side of the membrane, which typically is thepermeate side of the membrane. These membrane systems typically aredesigned to produce a pure oxygen product on the permeate side. If thesemembranes are used with low pressure air on the low pressure side of themembrane, the porous support layers on the low pressure side of themembrane introduce a gas phase diffusional resistance for transport ofoxygen from the oxidant or air to the surface of the dense separatinglayer. Porous layers that are thick enough to provide support for thethin active separating layer introduce diffusional resistance to thetransport of oxygen to the membrane surface, and this resistance willdecrease the oxygen flux through the membrane. A need exists, therefore,for composite membrane designs that use a thin active membrane under ahigh pressure differential without unacceptably high gas phasediffusional resistance on the oxidant side of the membrane.

Porous materials have lower mechanical strength than dense materials.Membrane designs that use porous supports on the low pressure side of amembrane subject the porous support to a compressive stress. This stressmay exceed the crush strength of the porous support layer if thedifferential pressure is high enough, causing the support layer to failand the thin active layer to leak or fail. The strength of a porouslayer is a function of the porosity of the layer material—a lowerporosity material is generally stronger than a higher porosity material.Unfortunately, a stronger material with a lower porosity is lesspermeable than a weaker material with a higher porosity, and increasingthe strength of a porous support layer thus increases the gas phasediffusional resistance of the layer. This tradeoff between strength andpermeability in porous support materials makes it difficult to designcomposite membranes that can withstand high pressure differentials andthe resulting high compressive stresses. Thus there is a need formembrane designs that avoid placing porous layers under high compressivestresses.

Oxygen transport through a dense oxygen-conducting ceramic membrane isthermally activated. This means that the oxygen flux through themembrane increases exponentially with temperature in the absence of anyother mass transfer resistances. When a dense oxygen-conducting membraneis used in a membrane reactor system to conduct an exothermic reactionsuch as hydrocarbon oxidation, the thermally activated oxygen transportcan lead to local hot spots on the membrane. A thin spot on the membranewill experience a higher oxygen flux relative to thicker surroundingregions on the membrane, and the membrane will heat up at this thin spotrelative to its surroundings as the oxidation rate increases. This willincrease the flux further, thereby further increasing the temperature atthat spot. These local temperature gradients generate undesirablethermal stresses that are detrimental to the mechanical integrity of themembrane.

There is a need in the ceramic membrane reactor field for a membranedesign capable of withstanding high pressure differentials while alsopreventing local hot spots from occurring. In particular, there is aneed for a hydrocarbon partial oxidation reactor membrane design thatwill allow the use of a thin oxygen-permeable membrane layer operatingunder a large pressure differential without developing hot spots causedby localized high oxygen diffusion and high exothermic oxidation rates.This need is addressed by the present invention as described below anddefined by the claims that follow.

BRIEF SUMMARY OF THE INVENTION

One embodiment of the invention relates to a planar ceramic membraneassembly comprising a dense layer of mixed-conducting multi-componentmetal oxide material, wherein the dense layer has a first side and asecond side, a porous layer of mixed-conducting multi-component metaloxide material in contact with the first side of the dense layer, and aceramic channeled support layer in contact with the second side of thedense layer. The dense layer and the porous layer may be formed ofmulti-component metal oxide material with the same composition. Thedense layer, the channeled support layer, and the porous layer may beformed of multi-component metal oxide material with the samecomposition.

In the planar ceramic membrane assembly, the mixed-conductingmulti-component metal oxide material may comprise one or more componentshaving the general composition (La_(x)Ca_(1-x))_(y)FeO_(3-δ) wherein1.0>x>0.5, 1.1≧y>1.0, and δ is a number which renders the composition ofmatter charge neutral. The porous layer may have a porosity betweenabout 10% and about 40% and a tortuosity between about 3 and about 10.

The porous layer may comprise one or more catalysts that include metalsselected from or compounds containing metals selected from the groupconsisting of platinum, palladium, rhodium, ruthenium, iridium, gold,nickel, cobalt, copper, potassium and mixtures thereof.

Another embodiment of the invention includes a planar ceramic waferassembly comprising

-   -   (a) a planar ceramic channeled support layer having a first side        and a second side;    -   (b) a first dense layer of mixed-conducting multi-component        metal oxide material having an inner side and an outer side,        wherein portions of the inner side are in contact with the first        side of the ceramic channeled support layer;    -   (c) a first outer support layer comprising porous        mixed-conducting multi-component metal oxide material and having        an inner side and an outer side, wherein the inner side is in        contact with the outer side of the first dense layer,    -   (d) a second dense layer of mixed-conducting multi-component        metal oxide material having an inner side and an outer side,        wherein portions of the inner side are in contact with the        second side of the ceramic channeled support layer; and    -   (e) a second outer support layer comprising porous        mixed-conducting multi-component metal oxide material and having        an inner side and an outer side, wherein the inner side is in        contact with the outer side of the second dense layer.

The thickness of the wafer assembly may be between about 2 and about 8mm as measured from the outer side of the first outer support layer tothe outer side of the second outer support layer. The thickness of eachof the first and second outer support layers may be between about 50microns and about 1 mm. The thickness of each of the first and seconddense layers may be between about 10 and about 500 microns. Thethickness of the planar ceramic channeled support layer may be betweenabout 100 and about 2000 microns.

An embodiment of the invention includes a planar ceramic wafer assemblycomprising

-   -   (a) a planar ceramic channeled support layer having a first        side, a second side, a periphery, and a plurality of flow        channels extending through the channeled support layer between        the first and second sides and extending from a first region        within the periphery to a second region within the periphery,        wherein the flow channels place the first region and the second        region in flow communication;    -   (b) a first dense layer of mixed-conducting multi-component        metal oxide material having an inner side and an outer side,        wherein the inner side is in contact with the first side of the        ceramic channeled layer;    -   (c) a first outer support layer comprising porous ceramic        material, the layer having an inner side, an outer side, and a        periphery, wherein the inner side is in contact with the outer        side of the first dense layer,    -   (d) a second dense layer of mixed-conducting multi-component        metal oxide material having an inner side and an outer side,        wherein the inner side is in contact with the second side of the        ceramic channeled layer;    -   (e) a second outer support layer comprising porous ceramic        material, the layer having an inner side, an outer side, and a        periphery, wherein the inner side is in contact with the outer        side of the second dense layer;    -   (f) a first opening extending through a layered assembly defined        by (a) through (e) from a first side to a second side of the        layered assembly, wherein the first side is defined by the outer        side of the first outer support layer and the second side is        defined by the outer side of the second outer support layer, and        wherein the first opening passes through the first region of the        channeled support layer and is in flow communication with the        plurality of flow channels in the channeled support layer; and    -   (g) a second opening extending through the planar ceramic wafer        assembly from the first side to the second side thereof, wherein        the second opening passes through the second region of the        channeled support layer and is in flow communication with the        plurality of flow channels in the channeled support layer.

The first and second outer support layers may comprise dense ceramicmaterial surrounding the first and second openings. The first and secondouter support layers may comprise dense ceramic material adjacent theperiphery.

Another embodiment of the invention relates to a ceramic membrane stackcomprising

-   -   (a) a plurality of planar ceramic wafer assemblies, each planar        ceramic wafer assembly containing a first multi-component metal        oxide and comprising        -   (1) a planar ceramic channeled support layer having a first            side, a second side, a periphery, and a plurality of flow            channels extending through the channeled support layer            between the first and second sides and extending from a            first region within the periphery to a second region within            the periphery, wherein the flow channels place the first            region and the second region in flow communication;        -   (2) a first dense layer of mixed-conducting multi-component            metal oxide material having an inner side and an outer side,            wherein the inner side is in contact with the first side of            the ceramic channeled layer;        -   (3) a first outer support layer comprising porous ceramic            material, the layer having an inner side, an outer side, and            a periphery, wherein the inner side is in contact with the            outer side of the first dense layer,        -   (4) a second dense layer of mixed-conducting multi-component            metal oxide material having an inner side and an outer side,            wherein the inner side is in contact with the second side of            the ceramic channeled layer;        -   (5) a second outer support layer comprising porous ceramic            material, the layer having an inner side, an outer side, and            a periphery, wherein the inner side is in contact with the            outer side of the second dense layer;        -   (6) a first opening extending through a layered assembly            defined by (1) through (5) from a first side to a second            side of the layered assembly, wherein the first side is            defined by the outer side of the first outer support layer            and the second side is defined by the outer side of the            second outer support layer, and wherein the first opening            passes through the first region of the channeled support            layer and is in flow communication with the plurality of            flow channels in the channeled support layer; and        -   (7) a second opening extending through the layered assembly            from the first side to the second thereof, wherein the            second opening passes through the second region of the            channeled support layer and is in flow communication with            the plurality of flow channels in the channeled support            layer; and    -   (b) a plurality of ceramic spacers, each spacer containing a        second multi-component metal oxide, wherein each spacer has a        first surface, a second surface generally parallel to the first        surface, a first manifold opening extending from the first        surface to the second surface and a second manifold opening        extending from the first surface to the second surface;        wherein the stack is formed by alternating ceramic spacers and        planar ceramic wafer assemblies in an axial direction such that        the first manifold openings in the spacers and the first        openings in the layered assemblies are aligned to form a first        manifold extending through the stack perpendicular to the planar        ceramic wafer assemblies, and such that the second manifold        openings in the spacers and the second openings in the layered        assemblies are aligned to form a second manifold extending        through the stack perpendicular to the planar ceramic wafer        assemblies.

The thickness of the wafer assembly may be between about 1.5 mm andabout 8 mm as measured in the axial direction from the outer side of thefirst outer support layer to the outer side of the second outer supportlayer. The distance between successive wafer assemblies in the axialdirection as defined by the thickness of the spacer assembly may bebetween about 0.5 mm and about 5 mm.

The ceramic membrane stack may further comprise a joint material at eachinterface between a planar ceramic wafer assembly and a ceramic spacer,wherein the joint material comprises at least one metal oxide having atleast one shared metal contained in at least one of the firstmulti-component metallic oxide and the second multi-component metallicoxide, and wherein the joint material has a melting point below asintering temperature of the first multi-component metallic oxide andbelow a sintering temperature of the second multi-component metallicoxide.

One aspect of the invention includes a planar ceramic channeled supportlayer assembly comprising

-   -   (a) a planar ceramic slotted support layer having a first        surface, a second surface, and an outer periphery, wherein the        slotted support layer includes        -   (1) a region defined by a right parallelogram enclosing a            first plurality of parallel slots passing through the            support layer and oriented parallel to a first side and an            opposing second side of the parallelogram,        -   (2) a second plurality of parallel slots that extend through            the support layer from the first side to the second side,            are perpendicular to the first plurality of parallel slots,            and are disposed between the periphery and the first side of            the parallelogram, and        -   (3) a third plurality of parallel slots that pass through            the support from the first side to the second side, are            perpendicular to the first plurality of parallel slots, and            are disposed between the periphery and the second side of            the parallelogram;    -   (b) a first planar ceramic flow channel layer in contact with        the first surface of the planar ceramic slotted support layer,        wherein the first planar ceramic flow channel layer includes a        plurality of parallel flow channels that extend therethrough,        and wherein the plurality of parallel flow channels are adjacent        to, perpendicular to, and in fluid flow communication with the        first plurality of parallel slots in the support layer;    -   (c) a second planar ceramic flow channel layer in contact with        the second surface of the planar ceramic slotted support layer,        wherein the second planar flow channel layer includes a        plurality of parallel flow channels that extend therethrough,        and wherein the plurality of parallel flow channels are adjacent        to, perpendicular to, and in fluid flow communication with the        first plurality of parallel slots in the support layer; and    -   (d) a first and a second series of parallel slots that pass        through the ceramic channeled support layer assembly formed by        the first planar ceramic flow channel layer, the support layer,        and the second planar ceramic flow channel layer, wherein        -   (1) the first and second series of parallel slots are            perpendicular to the plurality of parallel flow channels in            the first and second planar ceramic flow channel layers,        -   (2) the first series of parallel slots is disposed between            the periphery and the first side of the parallelogram and            the slots in the first series of parallel slots pass through            and intersect the second plurality of parallel slots            extending through the support layer, and        -   (3) the second series of parallel slots is disposed between            the periphery and the second side of the parallelogram and            the slots in the second series of parallel slots pass            through and intersect the third plurality of parallel slots            extending through the support layer;            wherein the slots in the first and second series of parallel            slots are in fluid flow communication with all slots in the            first planar ceramic flow channel layer, the support layer,            and the second planar ceramic flow channel layer.

The width of each slot in the first plurality of parallel slots in theplanar ceramic slotted support layer may be between about 0.2 and about2 mm and the distance between adjacent parallel slots in the firstplurality of parallel slots may be between about 0.2 and about 4 mm.

A process-related embodiment of the invention includes a hydrocarbonoxidation process comprising

-   -   (a) providing a planar ceramic membrane reactor assembly        comprising a dense layer of mixed-conducting multi-component        metal oxide material, wherein the dense layer has a first side        and a second side, a support layer comprising porous        mixed-conducting multi-component metal oxide material in contact        with the first side of the dense layer, and a ceramic channeled        support layer in contact with the second side of the dense        layer;    -   (b) passing a heated oxygen-containing oxidant feed gas through        the ceramic channeled layer and in contact with the second side        of the dense layer;    -   (c) permeating oxygen ions through the dense layer and providing        oxygen on the first side of the dense layer;    -   (d) contacting a heated hydrocarbon-containing feed gas with the        support layer wherein the hydrocarbon-containing feed gas        diffuses through the support layer; and    -   (e) reacting the hydrocarbon-containing feed gas with the oxygen        to yield a hydrocarbon oxidation product.

The hydrocarbon-containing feed gas may comprise one or more hydrocarboncompounds containing between one and six carbon atoms. Theoxygen-containing oxidant feed gas may be selected from the groupconsisting of air, oxygen-depleted air, and combustion productscontaining oxygen, nitrogen, carbon dioxide, and water. The hydrocarbonoxidation product may comprise oxidized hydrocarbons, partially oxidizedhydrocarbons, hydrogen, and water.

The oxygen-containing oxidant feed gas and the hydrocarbon-containingfeed gas may flow cocurrently through the ceramic membrane reactorassembly. The support layer may include one or more catalysts comprisingmetals selected from or compounds containing metals selected from thegroup consisting of platinum, palladium, rhodium, ruthenium, iridium,gold, nickel, cobalt, copper, potassium and mixtures thereof.

Another embodiment of the invention relates to a method of making agreen ceramic planar channeled support layer assembly comprising

-   -   (a) preparing a green ceramic planar slotted support layer        having a first surface, a second surface, and an outer        periphery, wherein the slotted support layer includes        -   (1) regions on the first and second surface, each region            defined by a right parallelogram within the outer periphery            wherein each parallelogram has a first side and an opposing            second side,        -   (2) a first plurality of parallel slots that extend through            the support layer from the first side to the second side,            are perpendicular to the first side of each parallelogram,            and are disposed between the periphery and the first side of            each parallelogram, and        -   (3) a second plurality of parallel slots that pass through            the support from the first side to the second side, are            perpendicular to the second side of each parallelogram, and            are disposed between the periphery and the second side of            each parallelogram;    -   (b) preparing a first and a second green ceramic planar flow        channel layer, each of which includes a plurality of parallel        flow channels that extend therethrough;    -   (c) placing the first green ceramic planar flow channel layer in        contact with the first surface of the green ceramic planar        slotted support layer such that the plurality of parallel flow        channels are oriented parallel to the first and second plurality        of parallel slots in the support layer and are disposed within        the region on the first surface defined by the right        parallelogram;    -   (d) placing the second green ceramic planar flow channel layer        in contact with the second surface of the green ceramic planar        slotted support layer such that the plurality of parallel flow        channels are oriented parallel to the first and second plurality        of parallel slots in the support layer and are disposed within        the region on the second surface defined by the right        parallelogram; and    -   (e) cutting a first and a second series of parallel slots        through the green ceramic planar channeled support layer        assembly formed by the first green ceramic planar flow channeled        layer, the green ceramic planar slotted support layer, and the        second green ceramic planar flow channeled layer, wherein        -   (1) the first and second series of parallel slots are            perpendicular to the plurality of parallel flow channels in            the first and second green ceramic planar flow channel            layers,        -   (2) the first series of parallel slots is disposed between            the periphery and the first side of the parallelogram and            the slots in the first series of parallel slots pass through            and intersect the first plurality of parallel slots            extending through the support layer,        -   (3) the second series of parallel slots is disposed between            the periphery and the second side of the parallelogram and            the slots in the second series of parallel slots pass            through and intersect the second plurality of parallel slots            extending through the support layer; and    -   (f) cutting a third series of parallel slots through the green        ceramic planar channeled support layer assembly formed by the        first green ceramic planar flow channeled layer, the green        ceramic planar slotted support layer, and the second green        ceramic planar flow channeled layer, wherein slots in the third        series of parallel slots are parallel to slots in the first and        second series of parallel slots and lie between the first and        second series of parallel slots;        wherein the slots in the first and second series of parallel        slots are in fluid flow communication with all slots in the        first green ceramic planar flow channel layer, the green ceramic        planar slotted support layer, and the second green ceramic        planar flow channel layer.

The ceramic multi-component metal oxide material may include one or morecomponents, and the material may have the general composition(La_(x)Ca_(1-x))_(y)FeO_(3-δ) wherein 1.0>x>0.5, 1.1≧y>1.0, and δ is anumber which renders the composition of matter charge neutral.

An alternative embodiment of the invention includes a planar ceramicmembrane assembly comprising a dense layer of mixed-conductingmulti-component metal oxide material, wherein the dense layer has afirst side and a second side, a porous layer of mixed-conductingmulti-component metal oxide material in contact with portions of thefirst side of the dense layer, a ceramic channeled support layer incontact with the second side of the dense layer, and a coating of porousmixed-conducting multi-component metal oxide material on the portions ofsecond side of the dense layer that are not in contact with the ceramicchanneled support layer.

The coating may include one or more oxygen reduction catalystscomprising metals selected from, or compounds containing metals selectedfrom, the group consisting of platinum, palladium, ruthenium, gold,silver, bismuth, barium, vanadium, molybdenum, cerium, praseodymium,cobalt, rhodium and manganese.

Another alternative embodiment of the invention includes a planarceramic wafer assembly comprising

-   -   (a) a planar ceramic channeled support layer having a first side        and a second side;    -   (b) a first dense layer of mixed-conducting multi-component        metal oxide material having an inner side and an outer side,        wherein portions of the inner side are in contact with the first        side of the ceramic channeled support layer;    -   (c) a first outer support layer comprising porous        mixed-conducting multi-component metal oxide material and having        an inner side and an outer side, wherein the inner side is in        contact with the outer side of the first dense layer,    -   (d) a second dense layer of mixed-conducting multi-component        metal oxide material having an inner side and an outer side,        wherein portions of the inner side are in contact with the        second side of the ceramic channeled layer;    -   (e) a second outer support layer comprising porous        mixed-conducting multi-component metal oxide material and having        an inner side and an outer side, wherein the inner side is in        contact with the outer side of the second dense layer; and    -   (f) a coating of porous mixed-conducting multi-component metal        oxide material on the portions of the inner sides of the first        and second dense layers that are not in contact with the first        and second sides of the ceramic channeled support layer.

The coating may include one or more oxygen reduction catalystscomprising metals selected from, or compounds containing metals selectedfrom, the group consisting of platinum, palladium, ruthenium, gold,silver, bismuth, barium, vanadium, molybdenum, cerium, praseodymium,cobalt, rhodium and manganese.

In another embodiment, the invention may include a method of making aplanar ceramic membrane assembly comprising

-   -   (a) providing a planar ceramic membrane structure comprising a        dense layer of mixed-conducting multi-component metal oxide        material, wherein the dense layer has a first side and a second        side, a porous layer of mixed-conducting multi-component metal        oxide material in contact with the first side of the dense        layer, and a ceramic channeled support layer in contact with        portions of the second side of the dense layer; and    -   (b) applying a coating of porous mixed-conducting        multi-component metal oxide material to portions of the surface        of the dense layer that are not in contact with the channeled        support layer.

A related embodiment includes a method of making a planar ceramic waferassembly comprising

-   -   (a) providing a planar ceramic wafer structure comprising        -   (1) a planar ceramic channeled support layer having a first            side and a second side;        -   (2) a first dense layer of mixed-conducting multi-component            metal oxide material having an inner side and an outer side,            wherein portions of the inner side are in contact with the            first side of the ceramic channeled support layer;        -   (3) a first outer support layer comprising porous            mixed-conducting multi-component metal oxide material and            having an inner side and an outer side, wherein the inner            side is in contact with the outer side of the first dense            layer,        -   (4) a second dense layer of mixed-conducting multi-component            metal oxide material having an inner side and an outer side,            wherein portions of the inner side are in contact with the            second side of the ceramic channeled layer; and        -   (5) a second outer support layer comprising porous            mixed-conducting multi-component metal oxide material and            having an inner side and an outer side, wherein the inner            side is in contact with the outer side of the second dense            layer;    -   (b) flowing a slurry of multi-component metal oxide powder        suspended in a liquid through the channeled support layer and        depositing a layer comprising the metal oxide powder and the        liquid on interior surfaces of the channeled support layer,        first dense layer, and second dense layer; and    -   (c) evaporating the liquid from the layer to form a coating of        the multi-component metal oxide powder on the interior surfaces        of the channeled support layer, first dense layer, and second        dense layer.

The method may further comprise partially sintering the coating byheating the planar ceramic wafer assembly to temperatures between 900°C. and 1600° C. for 0.5 to 12 hours.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an exemplary membraneassembly in an embodiment of the present invention.

FIG. 2 is a plan view of a flow channel layer for an exemplary membraneassembly that is an embodiment of the present invention.

FIG. 3 is an enlarged view of a flow channel region of the flow channellayer of FIG. 2.

FIG. 4 is a plan view of a slotted support layer for the exemplarymembrane assembly that is an embodiment of the present invention.

FIG. 5 is a plan view of a completed channeled support layer using thecomponents of FIGS. 2 and 4.

FIG. 6A is a plan view of a completed wafer assembly.

FIG. 6B is a plan view of an alternative completed wafer assembly.

FIG. 7A is a sectional view defined by Section 1-1 of FIGS. 6A and 6B.

FIG. 7B is a sectional view defined by Section 2-2 of FIGS. 6A and 6B.

FIG. 8A is a schematic side view of a ceramic spacer for use inembodiments of the present invention.

FIG. 8B is a schematic top view of the ceramic spacer of FIG. 8A.

FIG. 9A is a schematic front view of an exemplary membrane stack formedby alternating wafers and spacers.

FIG. 9B is a schematic side view of the stack of FIG. 9A.

FIG. 10 illustrates the oxidant and reactant gas flows in the exemplarystack of FIG. 9B.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the present invention provide hydrocarbon partialoxidation reactor membrane designs that allows the use of a thinoxygen-permeable membrane layer operating under a large pressuredifferential without developing hot spots caused by localized highoxygen diffusion and high exothermic oxidation rates. This can beaccomplished in part by providing significant diffusional resistance oneither the low pressure or oxidant side of the membrane or on the highpressure or reactant side of the membrane. By limiting the diffusionrate of either oxygen or reactants to the surfaces of the activemembrane layer, the development of hot spots on the membrane can bereduced or eliminated. A porous layer in contact with the activemembrane layer can provide means to limit this diffusion rate, and theporous layer may be placed on either or both sides of the activemembrane.

In embodiments of the present invention, the porous layer preferably isplaced on the side of the active membrane having the highest gas phasediffusivities. In membrane reactors for the oxidation of hydrocarbonsusing an air feed, for example, the gas on the hydrocarbon or reactantside of the membrane exhibits higher gas phase diffusivities in porousmedia than the gases on the oxidant or air side of the active membrane.Thus a porous support layer preferably is placed on the reactant side ofthe membrane to minimize gas phase diffusional resistances.

In a membrane reactor having a high differential pressure between thereactant and oxidant sides of the active membrane, wherein the pressureis higher on the reactant side, a porous layer on the oxidant side issubjected to higher compressive stresses than would occur if the poroussupport were placed on the reactant side of the active membrane. This isanother reason to preferably place the porous support layer on thereactant side of the active membrane. Placing the porous support on thereactant side of the membrane can control hot spots on the activemembrane while also minimizing compressive stresses on the porousmaterial.

The active dense membrane layer also should be supported on the oxidantside of the membrane. In embodiments of the present invention, this maybe accomplished by placing a ceramic channeled layer or channeledsupport layer on the oxidant side of the membrane wherein an oxidant,for example air, flows through channels formed in the channeled supportlayer and directly contacts the surface of the active membrane. Thus anembodiment of the present invention includes a membrane assembly with adense active layer having a porous support layer on one side and achanneled support layer on the other side. More particularly, oneembodiment of the invention includes a planar ceramic membrane assemblycomprising a dense layer of dense mixed-conducting multi-component metaloxide material, wherein the dense layer has a first side and a secondside, a porous layer of mixed-conducting multi-component metal oxidematerial in contact with the first side of the dense layer, and aceramic channeled layer or channeled support layer in contact with thesecond side of the dense layer. The mixed-conducting multi-componentmetal oxide material conducts both oxygen ions and electrons.

An embodiment of the invention is illustrated in FIG. 1, which is aschematic cross-sectional view (not necessarily to scale) of anexemplary membrane assembly that may be used in a hydrocarbon oxidationmembrane reactor. Active membrane layer 1 is a dense layer ofmixed-conducting multi-component metal oxide material and may have athickness in the range of about 10 μm to about 500 μm. One side of theactive membrane layer, which may be defined as the outer side, is incontact with and preferably bonded to porous support layer 3. The otherside of the active membrane layer, which may be defined as the innerside, is in contact with and preferably bonded to channeled layer orchanneled support layer 5 which comprises ceramic support ribs 7interspersed with oxidant flow channels 9 that extend through the layer.One side of porous support layer 3, which may be defined as the innerside, is in contact with the outer side of active membrane layer 1. Theother side of porous support layer 3 may be defined as the outer side.

In the present disclosure, the terms “channeled layer” and “channeledsupport layer” have the same meaning. By definition, a channeled layerhas channels or openings extending between the two surfaces of thelayer, and gas can flow freely through these channels. Typically, thechanneled layer is made of dense ceramic material. The terms “porouslayer” and “porous support layer” have the same meaning. The terms“support layer” and “outer support layer” have the same meaning anddefine a layer comprising porous ceramic material. The terms “porouslayer”, “porous support layer”, “support layer”, and “outer supportlayer” may be used interchangeably. The term “porous” applies tosintered or fired ceramic material or layers having through pores, i.e.,pores which are interconnected such that gas can flow through the layer.

For the membrane to operate, reactants must be supplied to both surfacesof the active membrane layer. An oxygen-containing oxidant feed gas issupplied to the inner surface of the active membrane layer and ahydrocarbon-containing gas is supplied to the outer surface of theactive membrane layer. The oxygen-containing oxidant feed gas may beselected from the group consisting of air, oxygen-depleted air, andcombustion products containing oxygen, nitrogen, carbon dioxide, andwater. The hydrocarbon-containing gas may comprise one or morehydrocarbon compounds containing between one and six carbon atoms.

The mass transport resistance to the surface of the active membranelayer can be lower when the surface is not covered with a porous supportlayer. Gaseous species permeating through a porous layer will encounterdiffusional resistance. Gas can flow freely through the channels in achanneled layer. The hydraulic diameter of the channels in a channeledsupport layer are typically 2 to 3 orders of magnitude larger than theaverage diameter of the pores in a porous support layer. The hydraulicdiameter of a channel with a rectangular cross section is defined as 4times the cross sectional area divided by the wetted perimeter.

The term “dense” refers to a ceramic material through which, whensintered or fired, a gas cannot flow. Gas cannot flow through denseceramic membranes made of mixed-conducting multi-component metal oxidematerial as long as the membranes are intact and have no cracks, holes,or imperfections which allow gas leaks. Oxygen ions can permeate denseceramic membranes made of mixed-conducting multi-component metal oxidematerial. The term “green ceramic” means a material comprising ceramicpowder before sintering or firing. Green ceramics additionally maycomprise organic binders, organic dispersants, or organic pore formers.The term “ceramic” used alone refers to the material after sintering orfiring.

Channeled support layer 5 may be made of mixed-conductingmulti-component metal oxide material and may have a typical thickness inthe range of about 100 μm to about 4 mm. Porous support layer 3 may havea thickness in the range of about 50 μm to about 1 mm, a porosity,defined as the volume fraction of pores, between about 10% and about40%, and a tortuosity, between about 3 and about 10. The tortuosity isdefined as the ratio of the gas phase diffusivity multiplied by theporosity divided by the measured effective diffusivity through theporous layer. A more detailed definition of tortuosity can be found inChemical Engineering Kinetics and Reactor Design by Charles Hill, JohnWiley and Sons, 1977, page 435.

When the membrane assembly is used in a hydrocarbon oxidation membranereactor wherein the reactant or hydrocarbon side is at a higher pressurethan the oxidant side, porous support layer 3 preferably is on thereactant side and channeled support layer 5 preferably is on the oxidantside. When the hydrocarbon oxidation membrane reactor is operated toconvert a methane feed gas to synthesis gas by reaction with oxygen froman air feed gas, porous support layer 3 preferably is on themethane/synthesis gas side and channeled support layer 5 preferably ison the oxidant or air side of active membrane layer 1.

The dense material in active membrane layer 1 may comprise amixed-conducting multi-component metal oxide compound having the generalformula (La_(x)Ca_(1-x))_(y)FeO_(3-δ) wherein 1.0>x>0.5, 1.1≧y>1.0, andδ is a number which renders the composition of matter charge neutral.

Any appropriate ceramic material can be used for porous support layer 3,and may be, for example, material of the same composition as that ofactive membrane layer 1. Preferably, porous support layer 3 is amixed-conducting multi-component metal oxide material. Any appropriateceramic material can be used for the structural members of channeledsupport layer 5, and this ceramic material may have, for example, thesame composition as that of active membrane layer 1. The material ofchanneled support layer preferably is a dense ceramic material. In oneembodiment, active membrane layer 1, porous support layer 3, andchanneled support layer 5 all may be fabricated of material having thesame composition.

Active membrane layer 1 optionally may include one or more oxygenreduction catalysts on the oxidant side. The catalyst or catalysts maycomprise metals selected from or compounds containing metals selectedfrom the group consisting of platinum, palladium, ruthenium, gold,silver, bismuth, barium, vanadium, molybdenum, cerium, praseodymium,cobalt, rhodium and manganese.

Porous support layer 3 optionally may include one or more catalysts topromote hydrocarbon oxidation and other reactions that occur in theporous layer. The catalyst or catalysts may be disposed on either orboth surfaces of porous support layer 3, or alternatively may bedispersed throughout the layer. The one or more catalysts may comprisemetals selected from or compounds containing metals selected from thegroup consisting of platinum, palladium, rhodium, ruthenium, iridium,gold, nickel, cobalt, copper, potassium and mixtures thereof.

If desired for structural and/or process reasons, an additional porouslayer may be disposed between active membrane layer 1 and channeledsupport layer 5.

Various tubular or flat plate membrane configurations may be envisionedwhich use the basic structural characteristics of the membraneillustrated in FIG. 1, and any of these various configurations areconsidered to be within the scope of embodiments of the presentinvention. Flat plate or planar membrane module configurations areparticularly useful in the application described above for hydrocarbonoxidation reactors.

One exemplary embodiment of the present invention is a planar ceramicwafer assembly comprising a planar ceramic channeled layer having afirst side and a second side, a first dense layer of mixed-conductingmulti-component metal oxide material having an inner side and an outerside, wherein the inner side is in contact with the first side of theceramic channeled layer, and a first porous ceramic layer ofmixed-conducting multi-component metal oxide material having an innerside and an outer side, wherein the inner side is in contact with theouter side of the first dense layer. This wafer assembly also includes asecond dense layer of mixed-conducting multi-component metal oxidematerial having an inner side and an outer side, wherein the inner sideis in contact with the second side of the ceramic channeled layer, and asecond porous layer of mixed-conducting multi-component metal oxidematerial having an inner side and an outer side, wherein the inner sideis in contact with the outer side of the second dense layer. The waferassembly in this embodiment thus has a central channeled layersandwiched between two active membrane layers, and the two activemembrane layers are sandwiched between two outer porous support layers.

In an alternative embodiment, a thin coating of porous mixed-conductingmulti-component metal oxide material (not shown) may be applied toportions of the surface of active membrane layer 1 that face oxidantflow channels 9, i.e., those portions of the surface of active membranelayer 1 that are not in contact with support ribs 7. This coatingincreases the active surface area of active membrane layer 1 andpromotes mass transfer at the interface between active membrane layer 1and the oxidant or oxygen-containing gas flowing through the oxidantflow channels. This coating additionally may coat the walls of supportribs 7. The coating may comprise one or more oxygen reduction catalystson the oxidant side. The one or more catalysts may comprise metalsselected from or compounds containing metals selected from the groupconsisting of platinum, palladium, ruthenium, gold, silver, bismuth,barium, vanadium, molybdenum, cerium, praseodymium, cobalt, rhodium andmanganese. Methods of applying this coating are described below.

The properties and characteristics of the components of the membraneassembly described above are typical of the dense layers, channeledsupport layers, and porous support layers of the embodiments describedbelow.

A description of the fabrication of this exemplary embodiment of aplanar ceramic wafer assembly begins with the channeled layer orchanneled support layer. This exemplary channeled support layer may befabricated from three planar components—a planar green ceramic slottedsupport layer and two identical planar green ceramic flow channellayers—wherein the slotted support layer is sandwiched between the flowchannel layers. This is illustrated below by describing each of theplanar components in turn.

FIG. 2 is a plan view (not necessarily to scale) of a flow channellayer. This layer is formed from planar dense green ceramic materialhaving a selected composition and may be square, rectangular, round, orany other appropriate shape. Flow channel layer 201 is rectangular andhas two rectangular channeled regions 203 and 205 formed therein. Eachchanneled region has a pattern of through channels passing through thelayer with a lattice of solid ribs formed between the channels. Thispattern is better illustrated in FIG. 3, which is a magnified plan view(not necessarily to scale) of the channels in regions 203 and 205 ofFIG. 2, showing a pattern of alternating open channels 301 formed byrepresentative alternating supporting ribs 303 that are parallel tothrough channels 301 and intermediate supporting ribs 305 that areperpendicular to through channels 301.

FIG. 4 is a plan view (not necessarily to scale) of a slotted supportlayer. This layer is formed from planar dense green ceramic materialhaving a selected composition and may be square, rectangular, round, orany other appropriate shape, and typically has a similar shape and outerperimeter dimensions as the flow channel layer of FIG. 2. Slottedsupport layer 401 has a first generally rectangular region containingparallel slots 403 passing through the layer between support ribs 405and a second generally rectangular region containing parallel slots 407passing through the layer between support ribs 409. Typically, the widthof support ribs 405 and 409 (or the distance between slots 403 and 407)is between about 0.2 and about 4 mm and the width of slots 403 and 407is between about 0.2 and about 2 mm.

Slotted support layer 401 also has a plurality of parallel slots 411passing through the layer that are perpendicular to parallel slots 403and disposed between one side of the first generally rectangular regionand outer periphery 413. Slotted support layer 401 also has a pluralityof parallel slots 415 passing through the layer that are perpendicularto parallel slots 403 and disposed between an opposite side of the firstgenerally rectangular region and outer periphery 417. Slotted supportlayer 401 also has a plurality of parallel slots 419 passing through thelayer that are perpendicular to parallel slots 407 and disposed betweenone side of the second generally rectangular region and outer periphery419. Slotted support layer 401 also has a plurality of parallel slots423 passing through the layer that are perpendicular to parallel slots407 and disposed between the opposite side of the second generallyrectangular region and outer periphery 425.

A slotted support layer, such as slotted support layer 401, issandwiched between two flow channel layers, such as flow channel layer201, to form an intermediate channeled support layer. In thisintermediate channeled support layer, alternating supporting ribs 303(FIG. 3) of flow channel layer 201 are supported by support ribs 405 and409. Intermediate supporting ribs 305 are superimposed on slots 403 and407 and are narrower than the width of parallel slots 403 and 407 suchthat neighboring channels 301 in the lengthwise direction can be in flowcommunication, i.e., intermediate supporting ribs 305 do not block orbridge slots 403 and 407.

The intermediate green ceramic channeled support layer formed by placinga slotted support layer between two flow channel layers is modified asillustrated in FIG. 5, which is a plan view (not necessarily to scale)of a completed channeled support layer 501. The modification comprisescutting parallel slots 503 and 505 on either side of rectangularchanneled region 507, wherein these slots are parallel to slots 403 and407 in the slotted support layer. These slots pass completely throughchanneled support layer 501 and therefore cut through and intersectslots 411 and 415 (FIG. 4) in the slotted support layer (not seen inFIG. 5). The modification also includes cutting parallel slots 509 and511 on either side of rectangular channeled region 513. These slots passcompletely through channeled support layer 501 and therefore cut throughand intersect slots 419 and 423 (FIG. 4) in the slotted support layer(not seen in FIG. 5).

Slots 503 and 505 therefore are in flow communication with slots 403(FIG. 4) and with the slots in rectangular channeled region 507, andalso with the other rectangular channeled region (not seen in this view)on the opposite side of channeled support layer 501. In addition, slots509 and 511 therefore are in flow communication with slots 407 (FIG. 4)and with the slots in rectangular channeled region 513, and also withthe other rectangular channeled region (not seen in this view) on theopposite side of channeled support layer 501.

In an alternative method of making an intermediate green ceramicchanneled support layer, slots 403 and 407 are not cut initially inlayer 401 (FIG. 4). Instead, a center layer similar to layer 401 (butwithout slots 403 and 407) is laminated between two layers 201 (FIG. 2)and then slots similar to slots 403 and 407 are cut completely throughthe center layer and the two outer layers 201.

The completed green ceramic channeled support layer 501 then is modifiedby placing a thin layer of a green ceramic material that is a precursorof the active membrane material (described earlier as active membranelayer 1 in FIG. 1) in contact with each side of support layer 501. Inone embodiment, a layer of a green ceramic material that is a precursorof the porous support layer described earlier is placed in contact witheach of the thin layers of the green ceramic material that is theprecursor of the active membrane material. In an alternative embodiment,a composite support layer of green ceramic material is placed in contactwith each of the thin layers of the green ceramic material that is theprecursor of the active membrane material.

Each of these composite support layers is formed by applying greenceramic tape that is a precursor of a dense ceramic material around theperiphery of the layer and across the center region of the layer to forma frame defining two windows that may approximately match the dimensionsof rectangular channeled regions 507 and 513 of the channeled supportlayer of FIG. 5. Green ceramic material that is a precursor of theporous support material is applied within these windows in contact withthe green ceramic material that is a precursor of the active membranematerial in contact with each side of support layer 501. These twoembodiments yield completed assemblies that define green ceramic waferassemblies having a central channeled layer sandwiched between twoactive dense membrane layers with two outer ceramic precursor supportlayers.

In the first of the above embodiments, the green ceramic wafer assemblyis completed as shown in FIG. 6A by cutting holes, for example, fourholes 601, 603, 605, and 607, completely through the center region ofthe wafer assembly. More than four holes may be used if desired. Hole601 intersects and is in flow communication with slots 503 and 509 (FIG.5). Likewise, hole 607 intersects and is in flow communication withslots 505 and 511 (FIG. 5). Holes 601 and 607 thus provide internalmanifolds in flow communication with slots 403 and 407 (FIG. 4) and withthe slots in rectangular channeled regions 507 and 513 (FIG. 5).

In the second of the above embodiments, the green ceramic wafer assemblyis completed as shown in FIG. 6B by cutting holes, for example, fourholes 609, 611, 613, and 615 completely through the center region of thewafer assembly. More than four holes may be used if desired. Hole 609intersects and is in flow communication with slots 503 and 509 (FIG. 5).Likewise, hole 615 intersects and is in flow communication with slots505 and 511 (FIG. 5). Holes 609 and 615 thus provide internal manifoldsin flow communication with slots 403 and 407 (FIG. 4) and with the slotsin rectangular channeled regions 507 and 513 (FIG. 5). In thisembodiment, regions 617 and 619 of the support layer contain the greenceramic material that is a precursor of the porous support material. Theremaining region of the support layer, i.e., the region surroundingholes 609-615, region 617, and region 619, contains the green ceramictape described above that is a precursor of a dense ceramic material.

These green ceramic wafer assemblies are then fired to sinter allceramic material in the assemblies. After firing, the internalconfigurations of the completed wafer assemblies in FIGS. 6A and 6Ballow gas to flow through hole 601 or 609, through slots 403 and 407 aswell as the slots in regions 507 and 513, thereby contacting the gaswith the surfaces of the two active dense membrane layers on either sideof central channeled support layer 501. After contact with the twoactive dense membrane layers, the gas flows into hole 607 or 615. Holes603 and 611, and holes 605 and 613, are not in direct flow communicationwith the internal slots and channels in channeled support layer 501,since these holes pass through the middle region of the support layerbetween slotted regions 507 and 513. Holes 603 and 605, or holes 611 and613, may serve as part of a stack flow manifold as described below.

The completed wafer assemblies of FIGS. 6A and 6B may have a widthbetween 5 and 40 cm, a length of between 5 and 40 cm, and a thicknessbetween 1.5 mm and 8 mm.

The internal structure of the wafer assemblies described above isillustrated in FIG. 7A, which shows (not necessarily to scale)representative internal section 1-1 of FIGS. 6A and 6B. Outer supportlayers 701 and 703 of porous ceramic material were described earlier asporous support layer 3 of FIG. 1. Active dense membrane layers 705 and707 were described earlier as active membrane layer 1 in FIG. 1. Slottedsupport layer 709 corresponds to slotted support layer 401 of FIG. 4 andshows portions 711 of parallel support ribs 405 or 409 of FIG. 4. Alsoshown are representative open slots 713, which correspond to parallelslots 403 or 407 of FIG. 4.

Flow channel layers 715 and 717 correspond to the flow channel layer ofFIG. 2 and the enlarged view of FIG. 3. Representative open channels 719correspond to open channels 301 formed by alternating supporting ribs303 in FIG. 3. Representative intermediate supporting ribs 721 and 723correspond to intermediate supporting ribs 305 in FIG. 3. Representativeopen channels 725 are representative of open channels 301 formed byalternating supporting ribs 303 in FIG. 3. Representative intermediatesupporting ribs 727 and 729 correspond to intermediate supporting ribs305 in FIG. 3. Representative open slots 713 are wider than intermediatesupporting ribs 721, 723, 727, and 729, so that open channels 719 and725 are in flow communication via open slots 713.

The internal structure of the exemplary wafer assembly described aboveis further illustrated in FIG. 7B, which shows (not necessarily toscale) a representative internal section 2-2 of FIGS. 6A and 6B. Outersupport layers 701 and 703 and active dense layers 705 and 707 areidentical to those of FIG. 7A. Section 2-2 shows a longitudinal view ofslotted support layer 709, which view corresponds to longitudinalsection of a portion of slot 403 or 407 of FIG. 4.

Flow channel layers 715 and 717 correspond to the flow channel layer ofFIG. 2 and the enlarged view of FIG. 3. Section 2-2 shows a sectionacross open channels 301 and alternating supporting ribs 303 in FIG. 3.Porous support layers 701 and 703, as well as dense layers 705 and 707,are also shown in FIG. 7B.

In FIGS. 7A and 7B, a channeled support layer may be defined by slottedsupport layer 709 and flow channel layers 715 and 717. The channeledsupport layer has a first side defined by the interface between theinner side of dense layer 705 and flow channel layer 715. The channeledsupport layer has a second side defined by the interface between theinner side of dense layer 707 and flow channel layer 717. Portions ofdense layer 705 are in contact with alternating supporting ribs 303 andother portions are not in contact with these ribs. Also, portions ofdense layer 707 are in contact with alternating supporting ribs 303 andother portions are not in contact with these ribs. Thus only portions ofa dense layer are in actual contact with a side of a channeled supportlayer and the remaining portions of the dense layer are not in actualcontact with the channeled support layer.

In an alternative embodiment, a thin coating of porous mixed-conductingmulti-component metal oxide material (not shown) may be applied toportions of active dense membrane layers 705 and 707 that face openchannels 719 and 725 (FIG. 7A) and open channels 301 (FIG. 7B). Theseportions are the portions of active dense membrane layers 705 and 707that are not in contact with intermediate supporting ribs 721, 723, 727,and 729 (FIG. 7A) and alternating support ribs 303 (FIG. 7B). Thiscoating increases the active surface area of active dense membranelayers 705 and 707 and promotes mass transfer at the interface betweenactive dense membrane layers 705 and 707 and the oxidant oroxygen-containing gas flowing through the oxidant flow channels. Thecoating may comprise one or more oxygen reduction catalysts on theoxidant side. The one or more catalysts may comprise metals selectedfrom or compounds containing metals selected from the group consistingof platinum, palladium, ruthenium, gold, silver, bismuth, barium,vanadium, molybdenum, cerium, praseodymium, cobalt, rhodium andmanganese.

The coating may be applied by flowing a slurry of multi-component metaloxide powder through the channels of the wafer after the wafer has beenassembled, either in the green state or after sintering. The slurry maybe made by mixing multi-component metal oxide powder with a liquid suchas water or an organic solvent. Dispersants optionally may be added tothe slurry to stabilize the dispersion of the powder. Pore formingagents such as microcellulose or graphite may be added to the slurry toaid in the production of porosity. The slurry then is forced to flowthrough the wafer channels, filling the channels with the slurry. Theliquid from the slurry then is evaporated from the inside of the waferby heating the wafer. This leaves a coating of the multi-component metaloxide powder on the inside surface of the dense layer as well as thewalls of the channels of the channeled support layer. Alternatively, airor another gas is blown through the channels after the slurry has filledthe channels to force out excess slurry, leaving a coating of the slurryon the inside surface of the dense layer as well as the walls of thechannels of the channeled support layer. The slurry then is dried byheating the wafer to remove the liquid.

The multi-component metal oxide powder then is partially sintered tobond the powder to the inside surface of the dense layer. Sintering ofthe coating is accomplished by first heating to remove any liquid ororganics that were present in the slurry. The temperature is thenincreased to a level sufficient to partially sinter the powder andproduce a well adhered porous coating of multi-component metal oxide tothe inside surface of the dense layer. Typical conditions are 900-1600°C. for 0.5-12 hours. The porous coating may be 1 to 100 μm thick andpreferably may be <50 microns thick. The porous coating may be 10-50%porous and preferably may be 25-50% porous.

The complete wafer assembly described in FIG. 4, 5, 6A or 6B, 7A, and 7Bforms one of the basic repeating elements for a multi-wafer stack. Theother repeating element is the ceramic spacer shown in the views ofFIGS. 8A and 8B. The ceramic spacer is made of a selected ceramicmaterial, has openings 801 and 803 separated by rib 805, and has a widthsimilar to the width of the wafer assembly of FIGS. 6A and 6B. Theceramic material should be dense and non-porous so that gas cannot flowthrough the spacer walls surrounding openings 801 and 803. Opening 801is sized to fit over holes 601 and 603 of FIG. 6A or holes 609 and 611of FIG. 6B. Opening 803 is sized to fit over holes 605 and 607 of FIG.6A or holes 613 and 615 of FIG. 6B. The height of the spacer (thevertical dimension in FIG. 8A) may be in the range of 0.5 mm to 5 mm.

A plurality of wafer assemblies and spacers can be fabricated into aceramic membrane stack having alternating wafers and spacers as shown inthe front and side views of FIGS. 9A and 9B, respectively. This ceramicstack can be fabricated by assembling green ceramic components andfiring the resulting green stack assembly, or alternatively by firingindividual green ceramic components and joining the fired componentswith a joining compound as described below.

The views of FIGS. 9A and 9B illustrate the placement of stackcomponents and are not to scale. FIG. 9A shows a plurality of parallelwafer assemblies 901 and spacers 903 stacked congruently and inalternating fashion along axis 905. The wafer assemblies are supportedin the center of the stack by the spacers and are cantilevered out tothe edges of the stack. Optionally, spacers 907 can be placed betweenthe wafers on opposites sides of the stack as shown to provide supportand reduce the bending moment on the wafers near the central spacers.These spacers may extend across the full width of the stack, i.e.,extending perpendicularly into the page in FIG. 9A. Cap 909 is placed onthe top wafer of the stack to close holes 601, 603, 605, and 607 (FIG.6A) or holes 609, 611, 613, and 615 (FIG. 6B).

FIG. 9B shows a side view of the stack having wafers 901, spacers 907,and cap 909. This view corresponds to a vertical edge view of the waferin FIGS. 6A and 6B. Openings 911 (each of which corresponds to opening801 of the spacer in FIGS. 8A and 8B) and holes 601 and 603 (FIG. 6A) orholes 609 and 611 (FIG. 6B) form an internal manifold extending throughthe length of the stack. Likewise, openings 913 (each of whichcorresponds to opening 803 of the spacer in FIGS. 8A and 8B) and holes605 and 607 (FIG. 6A) or holes 613 and 615 (FIG. 6B) form an internalmanifold extending through the length of the stack. These two internalmanifolds are in flow communication through the wafers via the internalslots and channels in the channel support layer as earlier described. Acomplete stack, a portion of which is shown schematically in FIGS. 9Aand 9B, may contain between 1 and 200 wafers and may have a height of2.5 mm to 2.6 m. When assembled from green ceramic stack components, thestack described above may be sintered by firing at temperatures in therange of 1000-1600° C. for 0.5 to 12 hours.

Alternatively, the stack described above may be fabricated by firstassembling a plurality of individual green wafers as described above,making a plurality of green spacers as described above, and sinteringthese individual green ceramic wafer and spacer subcomponents attemperatures from 1000-1600° C. for 0.5 to 12 hours. The wafersubcomponents may comprise a first multi-component metallic oxide havinga first crystal structure selected from the group consisting of aperovskitic structure and a fluorite structure and the spacersubcomponent may comprise a second multi-component metallic oxide havinga second crystal structure identical to the first crystal structure. Thefirst and second multi-component metallic oxide compositions may be thesame. In an exemplary stack assembly, the wafer and spacer subcomponentsboth may have a composition defined by the formula(La_(0.85)Ca_(0.15))₁₀₁FeO₃.

Sintered wafer and spacer subcomponents then may be assembled into astack as described above with reference to FIGS. 9A and 9B by applyingat each interface between a wafer and a spacer a joint materialcomprising at least one metal oxide. The at least one metal oxide maycomprise at least one shared metal contained in at least one of thefirst multi-component metallic oxide and the second multi-componentmetallic oxide. The joint material preferably is free of carbon,silicon, germanium, tin, lead, phosphorus and tellurium. The at leastone metal oxide in the joint material preferably has a melting pointbelow the sintering temperature of the first multi-component metallicoxide and below the sintering temperature of the second multi-componentmetallic oxide. The stack formed in this manner is heated to atemperature above the melting point of the at least one metal oxide inthe joint material, below the sintering temperature of the firstmulti-component metallic oxide, and below the sintering temperature ofthe second multi-component metallic oxide. This yields a completed stackas described above with reference to FIGS. 9A and 9B.

In an exemplary method of making the gaskets described above, a slip wasmade by adding 920.2 grams of (La_(0.9)Ca_(0.1))_(1.005)FeO₃ powder and9.2 grams of Fe₂O₃ to a one-liter high density polyethylene containercontaining one kilogram of spherical zirconia media, 242.1 grams ofreagent grade toluene, 60.5 grams of denatured ethanol, and 4.65 gramspolyvinyl butyral. The slip was put on a paint shaker for 30 minutes.Plasticizer (53.56 grams butyl benzyl phthalate) and binder (48.9 gramsof polyvinyl butyral) were added to the slip and it was put back on thepaint shaker for an additional hour. The slip was rolled overnight and aviscosity of 1500 mPa-s was measured using a viscometer at 25° C. Theslip was then filtered, degassed, and cast on polyester to make driedtape approximately 250 μm thick. Gaskets with the appropriate shape anddimensions were sheared out of the tape and placed between the wafersand the spacers to be joined, thereby forming a stack. A pressure of 170kPa was applied to the joints and stack, and the assembly was slowlyheated to 1250° C. to remove the organics and sinter the joint compound,thereby forming a leak-tight stack.

Similar technology is disclosed in two copending applications filed oneven date herewith, one entitled “Method of Joining ITM Materials Usinga Partially or Fully-Transient Liquid Phase”, and having the AttorneyDocket No. 06272 USA, and the other entitled “Method of Forming aJoint”, and having the Attorney Docket No. 06067 USA.

In an alternative embodiment, a thin coating of porous mixed-conductingmulti-component metal oxide material may be applied to portions of theactive dense membrane layers in the completed ceramic stack of FIGS. 9A,9B, and 10. As described above for the wafer assemblies, this coating isapplied to the portions of the active dense membrane layers which facethe internal oxidant gas flow channels and which are not in contact withintermediate and alternating supporting ribs. In this embodiment, thecoating may be applied to the internal regions of the completed ceramicstack including the active dense membrane layers. This coating increasesthe active surface area of the active dense membrane layers and promotesmass transfer at the interface between active dense membrane layers andthe oxidant or oxygen-containing gas flowing through the oxidant flowchannels. The coating may comprise one or more oxygen reductioncatalysts on the oxidant side. The one or more catalysts may comprisemetals selected from or compounds containing metals selected from thegroup consisting of platinum, palladium, ruthenium, gold, silver,bismuth, barium, vanadium, molybdenum, cerium, praseodymium, cobalt,rhodium and manganese.

The coating may be applied by flowing a slurry of multi-component metaloxide powder through the channels of the stack after the stack has beenassembled. The slurry may be made by mixing multi-component metal oxidepowder with a liquid such as water or an organic solvent. Dispersantsoptionally may be added to the slurry to stabilize the dispersion of thepowder. Pore forming agents such as microcellulose or graphite may beadded to the slurry to aid in the production of porosity. The slurry isthen forced to flow through the channels in the stack, filling thechannels with the slurry. The liquid from the slurry then is drained andthe residual slurry inside the stack is dried by heating the stack. Thisleaves a coating of the multi-component metal oxide powder on all of theinside surfaces of the stack including the exposed dense layers.Alternatively, air or another gas may be blown through the channelsafter the slurry has filled the channels to force out excess slurry,leaving a coating of the slurry on the inside surface of the dense layeras well as the walls of the channels of the channeled support layers inthe stack. The slurry then may be dried by heating the stack to removethe liquid.

The multi-component metal oxide powder then is partially sintered tobond the powder to the inside surface of the dense layer. Sintering ofthe coating is accomplished by first heating the stack to remove anyliquid or organics that were present in the slurry. The temperature isthen increased to a level sufficient to partially sinter the powder andproduce a well-adhered porous coating of multi-component metal oxide onthe inside surfaces of the stack including the exposed surface portionsof the dense active layers. Typical conditions are 900-1600° C. for0.5-12 hours.

A plurality of completed ceramic stacks can be operated at temperaturesin the range of 650 to 1100° C. to convert a reactanthydrocarbon-containing feed gas and an oxygen-containing oxidant feedgas into a hydrocarbon oxidation product and unreacted feed gas. Thehydrocarbon-containing feed gas may comprise one or more hydrocarboncompounds containing between one and six carbon atoms. Theoxygen-containing oxidant feed gas may comprise air, oxygen-depletedair, or combustion products containing oxygen, nitrogen, carbon dioxide,and water. The hydrocarbon oxidation product may comprise oxidizedhydrocarbons, partially oxidized hydrocarbons, hydrogen, and/or water.In one exemplary application, the hydrocarbon-containing feed gas isnatural gas, the oxidant feed gas is a combustion product containingoxygen, nitrogen, carbon dioxide, and water, and the hydrocarbonoxidation product is synthesis gas containing hydrogen, carbon monoxide,carbon dioxide, and water.

The gas flows in an operating stack are illustrated in FIG. 10. Reactantgas containing hydrocarbon feed components flows into the stack andflows over the outer porous support layers of each wafer. Reactant gasand products exit the opposite side of the stack as shown. Oxidant gasenters at the bottom of the stack and flows upward through the firstinternal manifold, through the channeled support layer in each wafer,and downward through the second internal manifold. Oxygen-depletedoxidant gas leaves the stack as shown. The oxidant and reactant gasesthus flow through the stack cocurrently.

While the planar ceramic membrane components and stack described abovehave a rectangular configuration and each wafer has four active membraneareas, other features and configurations can be envisioned that wouldutilize the principles described above and would be included inembodiments of the present invention. Wafers may be square, round, orany other desired shape, and may have more than four or less than fouractive membrane areas. Other configurations of the channels in thechanneled support layer can be envisioned and would be included inembodiments of the present invention. Other internal manifoldconfigurations are possible within the scope of the invention and woulddepend on the wafer shape and number of active regions in each wafer.For example, the number and orientation of the slots and channels in thechanneled support layer as described above also may be varied to changethe structural and flow characteristics of the layer, and thesevariations would be considered within embodiments of the presentinvention.

1. A hydrocarbon oxidation process comprising (a) providing a planarceramic membrane reactor assembly comprising a dense layer ofmixed-conducting multi-component metal oxide material, wherein the denselayer has a first side and a second side, a support layer comprisingporous mixed-conducting multi-component metal oxide material in contactwith the first side of the dense layer, and a ceramic channeled supportlayer in contact with the second side of the dense layer; (b) passing aheated oxygen-containing oxidant feed gas through the ceramic channeledlayer and in contact with the second side of the dense layer; (c)permeating oxygen ions through the dense layer and providing oxygen onthe first side of the dense layer; (d) contacting a heatedhydrocarbon-containing feed gas with the support layer wherein thehydrocarbon-containing feed gas diffuses through the support layer; and(e) reacting the hydrocarbon-containing feed gas with the oxygen toyield a hydrocarbon oxidation product.
 2. The hydrocarbon oxidationprocess of claim 1 wherein the hydrocarbon-containing feed gas comprisesone or more hydrocarbon compounds containing between one and six carbonatoms.
 3. The hydrocarbon oxidation process of claim 2 wherein theoxygen-containing oxidant feed gas is selected from the group consistingof air, oxygen-depleted air, and combustion products containing oxygen,nitrogen, carbon dioxide, and water.
 4. The hydrocarbon oxidationprocess of claim 2 wherein the hydrocarbon oxidation product comprisesoxidized hydrocarbons, partially oxidized hydrocarbons, hydrogen, andwater.
 5. The hydrocarbon oxidation process of claim 2 wherein theoxygen-containing oxidant feed gas and the hydrocarbon-containing feedgas flow cocurrently through the ceramic membrane reactor assembly. 6.The hydrocarbon oxidation process of claim 2 wherein the support layercomprises one or more catalysts comprising metals selected from orcompounds containing metals selected from the group consisting ofplatinum, palladium, rhodium, ruthenium, iridium, gold, nickel, cobalt,copper, potassium and mixtures thereof.